Biological Macromolecules (College Board AP® Biology): Exam Questions

Biological macromolecules are essential for metabolism and energy storage. Carbohydrates, in particular, serve as primary sources of energy for many organisms. These molecules exist in different forms:

• A monosaccharide is a simple sugar composed of a single unit, e.g. glucose or fructose

• A disaccharide consists of two monosaccharide units joined by a covalent glycosidic bond, e.g. sucrose or maltose

• A polysaccharide is a long chain of many monosaccharide units, e.g. starch or cellulose

Scientists conducted an experiment to investigate the effect of different carbohydrate macromolecules on cellular respiration rates in yeast. They measured carbon dioxide (CO₂) production when yeast cells were exposed to different sugar sources.

Table 1: CO₂ production by yeast in the presence of different carbohydrates

Justify the role of the control in this experiment.

(i) Describe the relationship between number of covalent bonds and CO₂ production shown in Table 1.

(ii) Explain the relationship described in (i).

(i) Identify the carbohydrate source that resulted in the highest rate of respiration.

(ii) identify the carbohydrate source that resulted in the lowest rate of respiration.

(iii) Calculate the difference in CO₂ production between these two carbohydrate sources.

Raffinose is a trisaccharide molecule containing glucose.

(i) Predict the approximate rate of CO₂ production if raffinose was used as a carbohydrate source in this experiment.

(ii) Justify your prediction in (i).

Saliva samples are commonly used in genetic testing. The information in Table 1 details some of the key macromolecules found in saliva.

Table 1: Macromolecules found in saliva.

Identify the biological macromolecule that stores genetic information in saliva samples.

Explain how the structure of a nucleic acid allows information to be stored.

Amylase, lysozyme and peroxidase are all examples of enzymes involved in the digestion of food.

Explain why different types of enzyme are necessary.

Explain how the presence of bacterial DNA in saliva samples could affect genetic analysis.

Lipids play a critical role in cell membrane structure and function. The fluid mosaic model describes the plasma membrane as a dynamic structure, composed of phospholipids, proteins, cholesterol, and carbohydrates. The composition of lipids in the membrane can affect its fluidity and permeability. Figure 1. shows an image of the cell membrane

Describe the nature of the phospholipids seen in Figure 1.

Explain how the properties of phospholipids lead to the formation of the cell membrane structure in Figure 1.

Some phospholipids are saturated and some are unsaturated. A higher proportion of unsaturated phospholipids increases the fluidity of the membrane.

Predict how the composition of membrane lipids might change in organisms living in very cold environments.

Cell membrane fluidity is also influenced by the presence of cholesterol within the bilayer. Figure 2 shows the relationship between cholesterol and membrane fluidity at different temperatures.

Describe the relationship shown in Figure 2.

Liposomes are phospholipid vesicles that can be used in drug delivery systems; they encapsulate drug molecules to enhance their stability and bioavailability (the proportion of a drug that enters the bloodstream and reaches its target tissues). Liposomes can improve bioavailability by protecting drugs from degradation and enhancing cellular absorption. The ability of liposomes to maintain their structure over time and under different conditions, e.g. changing temperature and pH, determines how effectively they retain and deliver drugs before degrading.

Figure 1 shows a liposome carrying two different drug types.

(i) Describe how phospholipid properties allow liposome formation.

(ii) Explain how this can improve the bioavailability of a hydrophobic drug.

A PEGylated liposome is a phospholipid-based vesicle that has been modified by attaching polyethylene glycol (PEG) chains to its surface. Figure 2 shows a PEGylated liposome.

Scientists investigated how phospholipid composition and PEGylation affects liposome stability over time. Their findings are summarized in Table 1.

Table 1: Stability of liposomes with different phospholipid compositions over time.

(i) Identify the independent variables in this investigation.

(ii) Describe the effect that an independent variable has on liposome retention.

(iii) Explain the difference in liposome retention seen in liposomes that are high in saturated and high in unsaturated phospholipids.

A fever occurs when an individual has a core body temperature of over 37.8 °C.

(i) Describe the possible effect of a fever on liposome stability.

(ii) Explain how a fever may impact liposome retention.

Increased PEGylation enhances liposome stability, circulation time, and drug delivery efficiency by reducing recognition and clearance by the immune system.

To investigate how PEGylation affects drug bioavailability, researchers conducted an experiment using radioactively labeled drugs encapsulated in PEGylated and non-PEGylated liposomes. They then measured drug accumulation in target tissues using imaging techniques.

(i) Predict how increasing PEGylation would affect drug bioavailability.

(ii) Provide reasoning to justify your prediction.

Cells use three primary macromolecules (carbohydrates, lipids and proteins) as energy sources, breaking them down through distinct metabolic pathways to generate ATP, the cell’s primary energy currency. Carbohydrates are generally the first macromolecule to be metabolised, followed by lipids, and finally proteins, which are processed only when other sources are insufficient.

Scientists measured energy yield per macromolecule to compare their efficiency in energy production, considering both their energy content per gram and specific dynamic action (SDA). SDA is the percentage of energy gained from a molecule that is used up during its digestion, absorption, and processing for metabolism. Table 1 summarizes the energy values and SDA percentages for three key macronutrients.

Table 1: Energy values and SDA of macronutrients.

A student concluded from Table 1 that lipids provide the highest net energy yield.

Use data in Table 1 to justify the student's conclusion.

Figure 1 below shows deamination, a process that occurs in the liver after protein digestion.

Use Figure 1 to explain the higher SDA value for proteins shown in Table 1.

Using the data in Table 1, calculate the difference in net energy output between proteins and carbohydrates. Assume median SDA values for each molecule.

Scientists carried out an investigation into the effect of macronutrient composition on fat loss. Two groups of participants were placed on calorie-controlled diets: one high in protein, and the other high in carbohydrates. Each participant’s body fat mass was recorded weekly over an 8-week period. The results are shown in Figure 1.

Using all the data provided, explain why a high-protein diet leads to the fat loss trend seen in Figure 1.

DNA has an antiparallel double helix structure. The antiparallel nature of the complementary strands means that new strands are synthesized in opposite directions during DNA replication; the two new strands are known as the leading and the lagging strands.

A study investigated DNA replication efficiency in eukaryotic cells at different activity levels of two enzymes: DNA polymerase α (Pol α) and DNA polymerase δ (Pol δ). The results are shown in Table 1.

Table 1: DNA replication efficiency at different levels of enzyme activity.

Explain the characteristic of enzymes that means Pol α and Pol δ both synthesize DNA in the 5' to 3' direction only.

Explain how the data in Figure 1 shows that both enzymes are required in DNA replication.

Some scientists claimed that other DNA polymerases may contribute to DNA replication.

Use the data in Table 1 to support this claim.

Explain how the structure of DNA ensures that genetic information is conserved through many generations of living organisms.